This invention relates in general to the manufacture of electromagnetic coil assemblies adapted for use in electric motors. More specifically, this invention relates to an improved structure for a bobbin which is adapted to have one or more windings of an electrical conductor wound thereabout to form an electromagnetic coil assembly.
Electric motors are well known devices which convert electrical energy to rotary mechanical energy. To accomplish this, electric motors establish and control electromagnetic fields so as to cause the desired rotary mechanical motion. There are many different types of electric motors, each utilizing different means for establishing and controlling these electromagnetic fields. Consequently, the operating characteristics of electric motors vary from type to type, and certain types of electric motors are better suited for performing certain tasks than others.
Synchronous motors constitute one principal class of electric motors. The two basic components of a synchronous motor are (1) a stationary member which generates a rotating electromagnetic field, generally referred to as the stator, and (2) a rotatable member driven by the rotating magnetic field, generally referred to as the rotor. Synchronous motors are characterized in that the rotational speed of the rotor is directly related to the frequency of the electrical input signal applied thereto and, therefore, the rotational speed of the electromagnetic field generated thereby. Thus, so long as the frequency of the applied electrical input signal is constant, the rotor will be driven at a constant rotational speed. Within this broad definition, however, the structure and operation of synchronous electric motors vary widely.
One variety of synchronous electric motor is a variable reluctance motor. Variable reluctance motors operate on the principle that a magnetic field which is created about a component formed from a magnetically permeable material will exert a mechanical force on that component. This mechanical force will urge the component to become aligned with the magnetic flux (lines of force) generated by the magnetic field. Thus, by using the stator to establish and rotate a magnetic field about a rotor formed from a magnetically permeable material, the rotor can be driven to rotate relative to the stator. The resistance to the passage of this magnetic flux from the stator to the rotor is referred to as reluctance. The magnitude of this reluctance changes with the rotational position of the rotor relative to the stator. Thus, electric motors of this type are commonly referred to as variable reluctance motors.
In a basic variable reluctance motor structure, this operation can be accomplished by providing a generally hollow cylindrical stator having a plurality of radially inwardly extending poles formed thereon which extend longitudinally throughout the length thereof. Concentrically within the stator, a cylindrical rotor is rotatably supported. The rotor is provided with a plurality of radially outwardly extending poles which also extend longitudinally throughout the length thereof. The stator and the rotor are both formed from a magnetically permeable material. A winding of an electrical conductor is provided about each of the stator poles, extending longitudinally. However, no electrical conductor windings are provided on the rotor poles. By passing pulses of electrical current through each of the stator windings in a sequential manner, the stator poles can be selectively magnetized so as to attract the rotor poles thereto. Consequently, the rotor will rotate relative to the stator.
Another variety of synchronous electric motor is a synchronous inductor motor. Similar to the variable reluctance motors described above, synchronous inductor motors use the stator to establish and rotate a magnetic field about a rotor formed from a magnetically permeable material. However, rather than rely upon the rotor to move toward a position of minimum reluctance in the presence of this magnetic field, the synchronous inductor motor employs a permanent magnet to polarize the rotor poles. The permanently polarized rotor poles are then attracted and repelled from the selectively polarized stator poles to cause rotation of the rotor relative to the stator. Because this interaction between the two magnetic fields causes rotation of the rotor, synchronous inductor motors function somewhat similarly to conventional induction motors. As a result, synchronous inductor motors are often referred to as hybrid motors, exhibiting certain characteristics of both variable reluctance synchronous motors and induction motors.
To optimize the operation of the either variety of electric motor, the magnitude of the electrical current which is sequentially passed through the stator windings is typically varied as a function of the rotational displacement of the rotor, as opposed to simply being supplied in an on-off manner. For example, the magnitude of the electrical current passed through a particular stator winding can initially be large, but decrease as the rotor pole rotates toward it. Consequently, the stator winding is prevented from continuing to attract the rotor pole toward it when the rotor pole has rotated to a position near or adjacent to the stator pole. This facilitates the rotation of the rotor at a more uniform speed.
As discussed above, the windings of electric motors having this structural geometry extend longitudinally throughout the stator, each being disposed individually about respective ones of the stator poles. In some instances, the windings are made by simply winding the electrical conductor directly about each of the stator poles. In other instances, however, the windings are formed by winding the electrical conductor about a hollow bobbin. The bobbins are typically formed from an electrically non-conductive and non-magnetically permeable material, such as plastic, and provide structural support for the windings of the electrical conductor. After being wound with the electrical conductor, the bobbins are inserted within the interior of the hollow cylindrical stator, then moved radially outwardly so as to be disposed about each of the stator poles. In electric motors having this type of structural geometry, this assembly process of initially winding the bobbin with an electrical conductor and subsequently installing the wound bobbin about each of the longitudinally extending stator poles can be accomplished relatively quickly and easily.
However, such an assembly process is not well suited for electric motors having different structural geometries. For example, in some electric motors, it is desirable that the magnetic flux generated by the electromagnetic fields extend longitudinally throughout the stator and the rotor in a plane which is generally parallel to the longitudinal axis of the motor, not perpendicular as described above. In electric motors having this alternative structural geometry, the stator has a plurality of axially extending inner teeth formed thereabout. A cylindrical rotor assembly is supported concentrically within the stator for rotation relative thereto. The rotor assembly includes a shaft having a plurality of rotor pole sub-assemblies provided thereon. Each of the rotor pole sub-assemblies includes a hub secured to the shaft, a pair of annular rotor packs secured to the ends of the hub, and an electromagnetic coil disposed loosely about the hub between the two rotor packs. Each of the rotor packs has a plurality of axially extending outer teeth formed thereabout which are disposed adjacent to the inner stator teeth. The electromagnetic coils are engaged by the stator such that the rotor assembly is free to rotate relative thereto. The electromagnetic coils are sequentially energized and de-energized so as to create sequential magnetic circuits between each of the rotor pole sub-assemblies and the stator. These magnetic circuits sequentially cause the angularly offset teeth of the rotor packs to be attracted to the teeth of the stator, resulting in rotation of the rotor assembly relative to the stator.
The process of manufacturing a rotor pole sub-assembly for such an electric motor is relatively time-consuming and inefficient. Accordingly, it would be desirable to provide an improved structure for a bobbin which facilitates the assembly process and which permits a plurality of the windings to be formed simultaneously so as to reduce assembly time and increase efficiency.